Exhaust management control systems that use a hydrocarbon adsorber in connection with a conventional catalytic converter catalyst coated substrate have been proposed for use in vehicles with internal combustion engines. In general, the absorber is implemented to limit hydrocarbon emissions during and immediately following cold start operation of the vehicle engine. Cold start operation is engine start up when the engine (and the catalytic converter) are at temperatures below normal operating temperatures.
More particularly, when the vehicle engine is started, exhaust gases out of the engine travel through the exhaust manifold to a combination of a catalyst-coated substrate and an adsorber. The configuration of the catalytic converter substrate and the adsorber may vary and many different configurations are known. For example, the adsorber may be provided upstream of the catalytic converter substrate or between two catalytic converter substrates. In the first example, exhaust gases flowing out of the engine immediately after a cold start of the engine have their hydrocarbons removed by and stored in the adsorber. The exhaust gases then continue to the downstream catalytic converter and heat the converter to a light-off temperature, at which point the catalytic converter can provide conventional catalytic operation on the exhaust gases to reduce undesirable exhaust gas species to gas species more acceptable for vehicle tail pipe emissions. As the adsorber warms up, it begins to desorb the stored hydrocarbons, sending those hydrocarbons to the catalytic converter for conversion to the more desirable exhaust gases.
Ideally, the catalytic converter light-off occurs before significant desorption of the adsorber. In some examples, it may be beneficial to provide a second catalyst coated substrate upstream of the adsorber to ensure that light-off of the upstream catalytic converter catalyst coated substrate occurs before desorption from the adsorber. During desorption from the absorber, the engine operates in a lean mode or a supplemental air pump is used to pump supplemental air into the exhaust gas flow path upstream of the adsorber. The lean exhaust gas and/or supplemental air stimulate desorption of the hydrocarbons from the adsorber.
Another advantage of running the engine lean and/or providing supplemental air from an air pump during the desorption relates to deposits of carbon, also referred to as coke deposits, that tend to build up on the adsorber during operation of the engine soon after engine start up. The coke deposits may occur when the adsorber zeolite reaches a temperature of about 200 degrees C, where certain zeolites tend to polymerize or partially crystallize carbon in the exhaust hydrocarbons. A significant carbon-rich presence allowing the coke build-up occurs due to the fuel-rich engine operation that typically occurs during and immediately following engine start-up. Once the adsorber reaches a sufficiently high temperature, for example, 600 degrees C, the coke deposits are burned off of the adsorber by forcing fuel-lean exhaust or supplemental air into contact with the coke deposits. After a sufficient period of burn off and desorption, the engine is run in closed loop fuel control mode, where the engine exhaust is ideally maintained at about stoichiometric conditions. After the desorption, the adsorber is generally nonfunctional in managing the exhaust gases flowing out of the vehicle engine and its next operation occurs after the next cold start of the vehicle engine, after which the adsorber performs the steps of adsorbing the hydrocarbons, desorbing the hydrocarbons and having coke buildup removed therefrom.